1. Field of the Invention
The present invention relates to exposure data indicating means for the view-finders of cameras adapted for changeover of exposure control from shutter speed priority automatic diaphragm control mode to diaphragm priority automatic shutter speed control mode and vice versa.
2. Description of the Prior Art
In the past, the type of data indicated in the viewfinder has generally depended upon whether exposure control is to be effected in a shutter speed priority mode or in a diaphragm priority mode. For instance, in the shutter speed priority mode, it has been the general practice to indicate both the set shutter speed and a preset value of an objective lens in the view finder. In general, the f-number actually required for a set shutter speed is separately indicated in the view finder by means of an exposure meter, so that in the case of a shutter speed priority mode, no meaning is derived from an indication of the preset f-number of an interexchangeable lens.
The cameras disclosed in U.S. patent application Ser. No. 804,290 filed June 7, 1977 and assigned to the same assignee, however, are adapted for selectively allowing both diaphragm priority mode operation and shutter speed priority mode operation. In such cameras, the diaphragm ring is preset to the maximum f-number to enable an indication of an anticipated automatically controlled f-number during shutter speed priority operation. These cameras include a first transmitting system for transmitting information relating to the step-difference between a minimum f-number and a set f-number for an interexchangeable lens to the camera body, and a second transmitting system for transmitting information relating to the maximum f-number of the interexchangeable lens from the lens to the camera body. Thus, information relating to the minimum inherent f-number of the interexchangeable lens may be derived. In addition, based on the minimum f-number information thus derived, information relating to the intensity of light passed through a fully open aperture, set shutter speed, and set film sensitivity, anticipated f-number for automatic control may be indicated. With cameras of this type, it is desirable, in the case of shutter speed priority operational mode, that a set f-number be indicated within the view-finder for the purpose of drawing the attention of the photographer.
In the case of diaphragm priority mode operation, it has been customary to provide an indication of an anticipated automatically controlled shutter speed in the view-finder. In this respect it would be meaningless to also indicate a set shutter speed in the view-finder since this often would confuse the photographer.